1. Field of the Invention
The present invention relates to an anamorphic converter that projects an image at magnification ratios different from each other in a main magnification direction and a sub-magnification direction, and to an image projection system that includes the anamorphic converter.
2. Description of Related Art
In an image projection system that projects an image displayed on a display device through a projection lens to a screen, it is possible to widen a field angle in, for example, a horizontal direction in the time of image projection by disposing an anamorphic converter between the projection lens and the screen. It is possible to compose such an anamorphic converter by using, for example, a plurality of cylindrical lenses (U.S. Pat. No. 5,930,050) or by using a plurality of prisms (U.S. Pat. No. 6,678,095).
Assuming that two directions are perpendicular to each other in a plane that meets an optical axis, a cylinder lens does not have power in one direction, and a prism has no power in any of the two directions. Accordingly, in the anamorphic converters disclosed in U.S. Pat. Nos. 5,930,050 and 6,678,095, it is impossible to correct a distortion in the direction where there is no power. FIGS. 31 and 32 show distortions of a projected surface on a wide-angle side (w) and an telephoto side (t) respectively in a case where the anamorphic converters disclosed in U.S. Pat. Nos. 5,930,050 and 6,678,095 are used and an image displayed on a display device is projected onto a projected surface in a state where an upper end or a lower end of a display surface of the display device is substantially aligned with optical axes of the projection lens and the anamorphic converter. As shown in these figures, if the anamorphic converters in U.S. Pat. Nos. 5,930,050 and 6,678,095 are used, a distortion of the projected area becomes remarkable especially on the wide-angle side.
It is possible to correct a distortion of a projected area by using a curved screen that is formed into a cylindrical curved surface shape. However, in a curved screen, it is possible to correct a distortion in a horizontal direction (transverse line), but impossible to correct a distortion in a vertical direction (longitudinal line), which is insufficient correction of a distortion. Besides, because a curved screen is expensive, it is desirable to correct a distortion without using a curved screen.